Voice disorders affect millions of Americans and have been targeted as a national priority for investigation. The impact of voice disorders on quality of life is significant; the ability to work, relate to friends and family, participate in social activties, and simply engage in everyday life becomes effortful, if not impossible, when one's voice is impaired. The multi-factorial nature of voice disorders necessitates that clinicians understand how the larynx functions in order to make appropriate treatment decisions. During phonation, the larynx serves as an energy transducer, transferring aerodynamic energy in the form of subglottal pressure (Ps) and airflow into acoustic energy in the form of sound. Noninvasive aerodynamic assessment is an objective and quantitative method of evaluating the inputs to voice production. The proposed research has two interrelated parts. In part I, research will focus on improving three methods of aerodynamic measurement developed in our laboratory: airflow interruption; incomplete airflow interruption; and airflow redirection. These methods have all been demonstrated to be accurate. Modifications will be made to the devices to allow for measurement of phonation threshold flow and phonation threshold power, two new parameters proposed by our laboratory that have been experimentally shown to be valuable. Enhancing these devices with additions such as auditory feedback, visual feedback, cheek restraints, and modified analysis techniques will also be investigated, potentially reducing intrasubject variability. We will also determine the optimal interruption length for measurement of Ps and determine how interruption affects vocal fold vibration by combining our aerodynamic assessment devices with high-speed video imaging. Elicitation of a reflex has hindered the widespread clinical application of airflow interruption. Visualizing the vocal folds during airflow interruption will allow us to determine if this reflex occurs at the larynx and if so, its precise latency. Data from part I will allow for selection of an improved method of aerodynamic assessment. In part II, the optimal system developed in part I will be used to evaluate and compare treatments for common voice disorders. The effect of polyp and nodule size on aerodynamic parameters will be evaluated; how aerodynamic parameters change as lesion size decreases will also be investigated. Pre- and post-treatment aerodynamic assessment will be performed to determine the effect of Botox injections on spasmodic dysphonia. We will also compare several common treatments for vocal fold paralysis. Though numerous treatments are available, an optimal treatment has yet to be developed. Real-time intraoperative measurements of vocal efficiency will be investigated as a means to optimize medialization laryngoplasty and arytenoid adduction. We will also determine the diagnostic power of each aerodynamic parameter individually and all parameters collectively. Preliminary observations suggest that aerodynamic measurements can improve assessment of voice disorders. Thus, the potential to improve understanding of normal and disordered voice production is great.